1. Field of the Invention
This invention relates generally to methods and apparatus for adhering objects to glass surfaces, and more particularly to methods and apparatus for adhering mirror buttons to vehicle windshields.
2. Background of the Invention
Numerous approaches have been employed in the past to overcome the difficulties in adhering objects to glass surfaces. For instance, rear view mirrors in vehicles are frequently mounted on the inner surface of a glass windshield. For the purposes of this invention, the term "vehicle" includes any transportation device having a windshield, including, but not limited to, automobiles, motorcycles, trucks, airplanes, boats, or the like. Most conveniently, the rear view mirror is releasably mounted on a "button" (also referred to as a "base" or a "knob") that is permanently mounted directly on the windshield. For convenience, the term "button" will be used herein to include the terms "base" and "knob". Mirror buttons are typically manufactured from sintered stainless steel or cast zinc, or the like.
The button enables the rear view mirror to be removed and remounted on the windshield. Typically, the button is adhered by a layer of adhesive to the windshield. Although many types of adhesives may be employed, it has been found that heat activated adhesives are most effective in bonding the mirror button to the windshield with sufficient strength to permanently mount the mirror button and support the rear view mirror during use. This requires the application of heat and pressure to cure the heat activated adhesive.
Secure adherence of the rear mirror is compounded by the doubly concave curvature of the inner surface of the windshield. Conventional heat activated tapes also have the advantage of being thick enough (for instance, 0.3 m) to provide a sufficiently compliant mount to accommodate the curvature of the windshield. However, it has been observed that air bubbles may be trapped between the adhering layer on the button and the surface of the windshield. These air bubbles may be visible from the exterior of the windshield, and, at a minimum are cosmetically undesirable. While it may be possible to provide an opaque covering to the exterior of the windshield to mask the air bubbles, this adds expense and difficulty (e.g. alignment of the button and the opaque covering, or alternatively, the application of the opaque covering after application of the mirror button) to the mounting of the rear view mirror. The presence of the air bubbles may even significantly reduce the security of the adherence of the button to the windshield.
During initial production of an automobile, a windshield is typically placed in a sealed environment (e.g. an autoclave) and subjected to high levels of pressure and temperature. In addition, most automobile windshields have an inner and outer layer and a polymeric layer interposed between the inner and outer layers. During the exposure to the high pressure and temperatures, this polymeric layer is fused and becomes optically transparent. The fused polymeric layer is a safety layer to control pieces of the windshield after breakage of the windshield. An incidental effect of the autoclave is to simultaneously cure the heat activated adhesive and secure the button to the windshield, as well as to drive out any trapped air bubbles to adhere the button to the windshield. The windshield may be then be assembled into the vehicle with the mirror button.
However, it is sometimes necessary to replace a windshield, or a mirror button, on a vehicle. As previously mentioned, most conventional adhering systems require the application of heat and pressure while curing the adhesive. This may be somewhat inconvenient in locations outside of a manufacturing facility, and it is undesirable to maintain an inventory of windshields with mirror buttons preattached at the manufacturing facility. Preattaching the mirror buttons is made all the more inefficient by the variety of mirror button designs available for different vehicles. It would also be preferable to be able to mount the mirror button with a manually manipulable device on the interior of the windshield while the windshield is mounted in the vehicle, rather than removing the entire windshield to be placed in an autoclave. However, installation of the mirror button with the windshield in place on a vehicle is rendered somewhat more difficult by the normal location of the mirror button, which necessitates installation in a partially inverted position.
Therefore, it is desirable to provide a method and apparatus for quickly and efficiently adhering an object, such as a rear view mirror button, to a glass surface, such a vehicle windshield.